What is a rainbow?

The rainbow is an optical and weather phenomenon, occurring in the form of a characteristic multicolored arc resulting from the cleavage of visible light, usually solar radiation, refracting and reflecting inside numerous drops of water (eg rain or fog) with a spherical shape.

On the basis of geometrical optics you can explain the formation of the rainbow and some of its accompanying effects. Light, falling to the surface, delimiting transparent optical centers, partially reflects, and in part, going to the second medium, breaks down. The angle of refraction depends on the wavelength of the light, resulting in the white light splitting into the colored spectrum.

 

How are rainbows created?

The source of the light that causes the rainbow is usually the Sun, sometimes also the Moon – moon rainbows are formed then. Nevertheless, because the resolution of the human eye in low light conditions is not very good and man can not see colors in low light, the moon rainbow is usually seen as a white (not colorful) arc.

The rainbow effect can be seen everywhere, where there are drops of water in the air, illuminated by the sun’s rays, falling at the back of the observer, and the sun is at a relatively small height (angle to a level less than 40 °). At higher altitudes the rainbow can be observed when the drops forming it are below the horizon, eg in the mountains or from the plane. The condition for obtaining a clear rainbow is lighting raindrops (clouds) through a parallel beam of sunlight and no scattered light.

The rainbow is also formed by waterfalls or fountains around which there are drops of water. The characteristic rainbow effects can also sometimes be noticed when the clouds are highlighted as vertical bands at distant rains or virgas, and can also be „artificially” obtained by spraying drops of water in the air lit by a strong unidirectional white light.

 

What are the colors of the rainbow?

The rainbow is undoubtedly one of the most beautiful optical phenomena on Earth. In this phenomenon, almost the entire color palette appears.

Despite the fact that there is an almost continuous spectrum of colors in the rainbow, the following colors are usually listed: red (outside the arch), orange, yellow, green, blue, indigo and purple (inside the arch).

 

What causes a double rainbow

Many times in the sky we can observe the second rainbow arc, located directly above the first one. This happens as a result of the double refraction of light inside the drops of water. Reflected light emerges from the drop at an angle of 51 degrees (this is the angular width of the secondary arc). As a result of the two incomplete reflection of light, the secondary rainbow is inverted compared to the actual rainbow. The intensity of colors in the „newly” created rainbow is smaller each time than in the original one.